draft design

codecs-sync-design.md

+### draft design for new codec sync with terminal capabilities.
+
+#### outgoing calls
+```mermaid
+sequenceDiagram
+    participant A as voicemngr
+    participant B as chan-voicemngr
+    A->>B: init call
+    Note over B: chan_voicemngr_start_calling/chan_voicemngr_new: <br/> require and wait for endpoint cap by ubus_invoke
+    B->>A: ubus_invoke(ubus_request_endpoint_codec_cap)
+    A->>B: ubus_send_reply(with codec_cap list)
+    Note over B: chan_voicemngr_start_calling/chan_voicemngr_new: <br/> update cap and continue with outgoing process
+```
+
+#### incoming calls
+```mermaid
+sequenceDiagram
+    participant A as asterisk/pjsip
+    participant B as chan-voicemngr
+    participant C as voicemngr
+    Note left of A : Incoming call
+    Note over A: incoming codec offer negotiation with pjsip cap <br/> and keep the list which used for calling chan_voicemngr
+    A->>B: chan_voicemngr_new(..., codec_list)
+    Note over B: chan_voicemngr_new: <br/> require and wait for endpoint cap by ubus_invoke
+    B->>C: ubus_invoke(ubus_request_endpoint_codec_cap)
+    C->>B: ubus_send_reply(with codec_cap list)
+    Note over B: chan_voicemngr_new: <br/> update cap and continue with incoming process, hangup chan if no shared cap
+    B->>A: cap update and continue with incoming process
+
+```
+
+### Tasks need to be done
+#### voicemngr
+ - init with endpoint capabilities(config file or get from endpoint).
+ - get dect cap while handset register
+ - new ubus method, ubus_request_endpoint_codec_cap
+
+
+#### chan-voicemngr
+ - get terminal cap while creating new call
+```
+chan_voicemngr_new(..., struct ast_format_cap *format){
+    ...
+    
++   ret = ubus_invoke(..,ubus_request_endpoint_codec_cap,..)
+    if (format) {
+-		ast_format_cap_append_from_cap(caps, format, AST_MEDIA_TYPE_UNKNOWN);
++       incoming call: check with the endpoint codec cap and update the incoming cap, hangup chan if no shared cap.
+	} else {
+-		ast_format_cap_append_from_cap(caps, default_cap, AST_MEDIA_TYPE_UNKNOWN);
++       outgoing call: using the endpoint codec cap instead of default_cap
+	}
+	...
+}
+```
+
+#### asterisk/pjsip
+ - keep incoming codecs offer list(only first in the list is kept at the moment) after negotiation with pjsip codec config(pjsip_endpoint.conf, uci sip_service_provider.codec_list) and call chan_voicemngr_new with the cap_list
+ - make sure that updated cap from chan-voicemngr is ready before 200OK response, and has been used in the 200OK correctly.
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